1. Field of the Invention
The present invention relates to a photodetector, a photosensing position detector, a coordinate input device, a coordinate input/output device, and a photodetection method.
2. Description of the Related Art
Some known coordinate input devices input two-dimensional coordinates on a screen of a large-scale display device by using a pointer, thereby entering drawings, characters or commands for controlling a system to an externally connected CPU (Central Processing Unit). Another known coordinate input device inputs three-dimensional coordinates by manipulating a pointer in a three-dimensional space, thereby entering a path of three-dimensional motion, information of the presence of an object, or commands for controlling a system.
Specifically, a coordinate input device for a large-scale display picks up a light spot on a screen using a CCD area sensor or a CCD linear sensor, and determines the position of the focused light spot on the sensor screen in response to an output signal thereof. The two-dimensional coordinates of the position on the screen are thus obtained. In yet another known coordinate input device, a plurality of position detector elements (a device that results in an analog output voltage in response to the position of the spot) are used to determine a two-dimensional coordinate position on the screen using the magnitude of the analog voltage or the ratio of the analog voltage.
The following three-dimensional coordinate input devices are known.
1) A coordinate input device that detects a three-dimensional motion or position by sensing a mechanical touch, mechanical deformation, or a kinetic acceleration with a sensor supported by a multi-articulate mechanism.
2) A coordinate input device that provides three-dimensional inputs by combining two-dimensional inputs from a joystick, etc.
3) A coordinate input device that determines three-dimensional input information by obtaining a stereo image with a plurality of video cameras sensitive to visible light or infrared light, and by processing the stereo image.
These coordinate input devices have to achieve the following goals.
A first goal to be addressed is to exclude the influence of interfering external light that has adverse effects in the determination of precise coordinates and a stable operation of the device.
The diversification of display types, the availability of infrared light as a wireless communication means, and the widespread use of infrared remote controllers makes infrared light ubiquitous in the environment where coordinate input devices are operated. There is a need for effective interfering light removal means.
A second goal is to achieve a wide dynamic range of receivable light. In the coordinate input device of the type that a user inputs coordinates by directing a light beam using a pointer, the amount of directed light greatly changes depending on the manipulation of the pointer (specifically, depending on the position of, the alignment of, and the speed of motion of the pointer). When the pointer is operated from a battery, the amount of directed light greatly varies depending on power remaining in the battery. The coordinate input device therefore needs photoreceving means having a wide dynamic range.
In this type of conventional coordinate input device, a light spot on a screen or in a three-dimensional space is picked up using a CCD area sensor or a CCD linear sensor, the focused position of the light spot on the sensor is determined from the output signal therefrom, and two-dimensional coordinates on the screen or three-dimensional coordinates in the three-dimensional space are thus determined. This conventional coordinate input device uses an optical filter for allowing light within a particular wavelength band to be transmitted as a means for removing interfering light. Tracking means for tracking variations in an amount of light is virtually unavailable. This means that the dynamic range of the device is narrow.
In another known coordinate input device, a plurality of position detector elements (a device that results in an analog output voltage in response to the position of the spot) is used to determine a two-dimensional coordinate position on the screen or a three-dimensional position in a work space using the magnitude of the analog voltage or the ratio of the analog voltage. This conventional coordinate input device uses an optical filter for allowing light within a particular wavelength band to be transmitted as a means for removing interfering light. Since means for detecting a received signal as coordinate information is used, tracking means for tracking variations in an amount of light is virtually unavailable.
The present invention provides a novel method for expanding dynamic range.
It is an object of the present invention to provide a photosensing position detector, a coordinate input device, and a coordinate input/output apparatus, each having a wide dynamic range.
A photodetector of the present invention includes a photoreceiving unit for receiving a light beam that blinks a plurality of times per detection period and converting the received light beam into a signal, and a signal processing and controlling unit for controlling the photoreceiving unit so that the signal that is output in response to the received light beam per blinking cycle of the light beam increases in strength as a blinking cycle count increases in each detection period.
A photosensing position detector of the present invention includes a line sensor, formed of pixels arranged in a line, for receiving a light beam that blinks a plurality of times per detection period, a signal processing and controlling unit which controls the line sensor so that the output signal of the line sensor in response to the received light beam per blinking cycle of the light beam increases in strength as the blinking cycle count increases in each detection period, and a determining unit which determines, as a photosensing position, the position of a pixel that generates a maximum value of the output signal.
Other features and advantages of the present invention will be apparent from the following description in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.